This invention relates to elevator safety systems and, more particularly, to systems for monitoring the inappropriate opening of an elevator hatch door.
The typical elevator system includes a vertical shaftway or hoistway that extends between several floors of a building, and a cab suspended from cables that cause the cab to travel up and down the shaftway on command. There are two types of elevator doors in any modern elevator system. A first door, called a hatch or shaftway door, is located at every floor and under normal operation it is opened only when an elevator is aligned with the particular floor and has completely stopped. The main purpose of the hatch door is to prevent people from falling down the shaft when the elevator is elsewhere within the shaftway. If, for example, the cab is on the first floor and the hatch door on the fifth floor is open or is at least unlocked, someone could walk into the shaftway and fall four floors onto the top of the cab, causing injury and even death. The hatch door also prevents injury to people on a floor who might be struck by the elevator as it passes the shaftway entrance on that floor. A closed shaftway door is a reminder to those people on a particular floor that the elevator cab is not ready to pick them up.
The second type of elevator door, a cab door, is similar to the shaftway door, but is located on the elevator cab itself. Under normal conditions, it is opened only when the cab is aligned with a floor. The purpose of the cab door is to protect the passengers on the moving elevator cab from injury due to contact with the parts of the shaftway which are otherwise exposed and accessible as the elevator cab ascends and descends within the shaftway.
Elevator systems are arranged so that all of the hatch doors are kept closed, except for the hatch door on the floor where the cab has stopped and is aligned with the hatch door. This is accomplished with electromechanical interlocks that prevent the shaft or hatch doors from being opened when no elevator is present. In fact, these interlocks are typically required by local law or ordinance.
The interlock may be in the form of a mechanical lever mounted in the shaft adjacent each hatch door. This lever is biased so that one end rotates into locking connection with the hatch door. The other end of the lever has a roller on it which engages a cam on the cab. As the cab approaches a floor, the cam causes the lever to rotate out of its locking position, permitting the hatch door on that floor to be opened. In addition to the mechanical interlock, the lever operates an electrical switch at each hatch door. The switches on each floor are connected in series and are part of the elevator control circuit in the machine or motor room on the roof. If a hatch door is opened by any means other than the cab, the electrical switch will open, which will cause the control circuit to stop the elevator and/or take it out of service. However, if the lever is in the door open position because the cab is at that floor, the switch at that floor is open, so there will be no signal taking the elevator out of service.
Some systems use the switch on the shaftway or hatch door to sound an alarm if the elevator moves away from a floor prior to the hatch door on that floor being fully closed (see U.S. Pat. No. 355,384 of Chinnock; U.S. Pat. No. 642,332 of Hunter and U.S. Pat. No. 777,612 of Eaton). Similarly, U.S. Pat. No. 3,091,760 of Spenard et al. discloses a burglar alarm switch assembly which is mounted along the inside surface of each sliding shaftway door to provide a signal when it is improperly opened.
Even though the interlocks are designed to provide some protection against accidental entry into an elevator shaft when the cab is not present, accidents still happen. The electromechanical interlocks are subject to repeated operation over years of operation. Also, an elevator shaft is a harsh environment, with water and debris falling down the shaft from time to time, and significate temperature conditions. As a result, the interlocks fail in ways that may be undetected by normal inspections and people continue to be injured.
The electromechanical hatch door interlocks help to prevent injury to building occupants engaged in normal use of elevators. However, in recent years injuries and death have resulted from the unauthorized use of elevators, particularly were individuals gain access to the top of the elevator cab and ride there for purposes of enjoyment or for purposes of extorting money from or robbing legitimate passengers. In particular, young children have been known to work together to gain access to the top of the elevator in order to ride there as a dangerous form of entertainment. Also, older individuals have gained access to the top of the elevator cab in order to extort money from passengers in the cab by disabling the elevator and refusing to restore service until they are paid. Further, some even employ weapons to rob the passengers. This situation has led to the injury and death of the people who ride on top of the elevator for enjoyment as well as to the victims of the people who gain access to the top of the elevator for purposes of robbery and extortion.
Unauthorized access to the top to the elevator or the shaft can be gained by stopping the elevator at one floor and attaching a rope of flexible metal wire to the interlock lever. Then an accomplice takes the elevator down one floor. The rope or wire is pulled, causing the lever to rotate as if the cab were at that floor. This opens the switch at that floor and releases the mechanical interlock for the hatch door on that floor. As a result, the hatch door on the floor above the cab can be open, thus allowing the individual to gain access to the elevator shaft or the top of the cab. The elevator control circuits are wired so that the elevator is returned to service as soon as the switch has been restored to it proper position, e.g., by closing the hatch door once the individual has gained access to the elevator shaft and to the top of the cab.
U.S. Pat. No. 3,677,370 of Devine discloses an elevator alarm system which sounds after the cab doors have been forced open between floors for a predetermined period of time. This patent describes the problem of people gaining access to the top of the elevator for purposes of robbery and extortion. The theory of this patent is that a robbery will require that the doors be open for some period of time, while a child opening the doors as a form of play will hold them open only for a few seconds. Therefore, a timed activation of the alarm can be used to distinguish a serious problem from less serious play. Thus, while recognizing the problem of unauthorized travel on an elevator, it does not prevent the problem.
A series of patents to Leone (i.e., U.S. Pat. Nos. 5,025,895; 5,283,400 and 5,347,094) describe the use of proximity detectors mounted on the top and bottom of elevator cabs to detect the presence of an intruder on those areas of the cab. Basically, the proximity detectors are aimed at the hatch doors on the floors above and/or below the cab. These detectors send out periodic pulses of light which are a few inches wide. These pulses are diffused off the hatch doors, typically the edge which first opens. The detector picks up the diffused light and measures the time it took for the light beam to travel to the door and return. Unless this is equal to or less than a prescribed period of time, an alarm condition is indicated. For example, if the door is opened, the beam either does not return or it takes longer to return because it must travel into the hallway adjacent the hatch door and strike a wall or some other object before returning to the detector. When an alarm condition is detected, an alarm siren is sounded, a warning strobe light is lit and the elevator is taken out of service. In this system the elevator remains out of service until restored by elevator personnel.
With the Leone system where only the door above or below the cab is monitored, individuals can go to the second floor above the cab, open that door and slide down the elevator cable to the top of the cab. To prevent this, additional monitors are used which sound an alarm only when the person is in the dangerous position of sliding down the cables. Triggering an alarm at that point might frighten them, causing them to fall.
It would be advantageous if a system were designed to provide improved protection to (i) building occupants from defective hatch door interlocks, which may allow them to fall into elevator shaftways, and from individuals bent on robbery or extortion; (ii) young children seeking thrills from riding on top of elevators; and (iii) building owners who are liable for the injuries to legitimate users of the elevators and perhaps even to those bent on larceny.